The purpose of this work is to determine the parameters of task-unrelated-thought-intrusions (TUTIs) both spontaneous (daydreams) and otherwise, as well as related mental activity such as insight, intuition, and mindwandering. An additional purpose is to investigate the relation between sustained attention and age. The purpose are accomplished through the use of retrospective questionnaires and by controlled laboratory manipulation. Outcomes derived from these purposes and obtained over this fiscal year were: (a) Three samples of men and women tested in 1962-64 and 1980-84 who ranged in age from 20 to 94 years and who performed the Mackworth Clock sustained vigilance task, were observed to show no statistically significant age differences in level of performance as measured by the percentage of targets detected, and by the mean response time for detected targets; this outcome represents one of the few that has failed to observe such performance differences when the full adult lifespan was sampled and strongly suggests an unchanged sustained attentional capacity for different age cohorts. (b) Four studies which varied the nature of the vigilance task and the method of determining TUTIs were carried out on men and women from 17 to 94 years of age. Three of these studies obtained an inverse relationship between the frequency of the TUTIs and the age of the participants. This finding was a laboratory corroboration of a previous finding which found an inverse relation between daydreaming frequency, as determined from a retrospective questionnaire, and age represented by the adult lifespan. These findings are interpreted in terms of reduced potency with increasing age of a thought-generating mechanism within the nonconscious mind.